Congruence and the Rigid Transformations

The Common Core State Standards call for teachers of geometry to radically change how they teach the topic of congruence. Key are the so-called Rigid Motions - flips, turns, and slides. In this pair of lessons, I define the Rigid Motions and then present the Rigid Motion Postulate, which states that the rigid motions preserve segment length and angle measure. Students are given opportunity to work with the Rigid Motions and are asked to prove a few simple congruence theorems.